Method and a device for improved status reports

ABSTRACT

A method for use in a cellular communications system in which system traffic can be exchanged between transceivers comprises receiving traffic from a second transceiver at a first transceiver. The traffic includes data units that are each associated with an identifier. The data units are also divided into segments. The method additionally includes sending status information from the first transceiver to the second transceiver. The status information pertains to one or more data units transmitted by the second transceiver. Additionally, sending the status information includes, for non-received and partially received data units, sending information indicating the data units were non-received or partially received and, for partially received data units, sending information indicating which parts of the data units were not received.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 13/269,338 filed on Oct. 7, 2011 which is a continuation ofU.S. patent application Ser. No. 12/524,891 filed on Jul. 29, 2009,which is the U.S. national stage entry of PCT/SE2008/050108, filed Jan.28, 2008, which claims the benefit of U.S. Provisional Application No.60/983,633, filed Oct. 30, 2007 and PCT/EP2007/050994 filed on Feb. 1,2007, the disclosures of which are all fully incorporated herein byreference.

TECHNICAL FIELD

The present invention discloses a method for use in a cellularcommunications system, in which system traffic can be exchanged betweena first and a second transceiver. The traffic is sent in data units,each of which is given an identifier and which may be divided intosegments. A receiving transceiver may send status information in dataframes or data units about transmitted data units to a transmittingtransceiver, i.e. to the transceiver from which the data wastransmitted.

BACKGROUND

In the 3GPP LTE project (3rd generation Partnership Project, Long TermEvolution) for cellular communication systems, an RLC (Radio LinkControl) protocol is used for communication between users in a cell andthe controlling node of the cell, i.e. the so called eNodeB, “evolvedNodeB”.

In the RLC, traffic is sent as so called PDUs, i.e. Protocol Data Units,which are identified by being given sequence numbers. In response toPDUs from a transmitting party, the receiving party sends so called RLCstatus PDUs to the transmitting party, with so called ACKs and/or NACKS,i.e. acknowledgements (ACK) that data has been properly received, orinformation (NACK) that data has not been properly received, i.e.received only partly or not at all. The ACKs and NACKS in the RLC statusPDUs are sent as PDU sequence numbers, in order to identify the PDU inquestion.

In LTE systems, RLC PDUs may be segmented, which has as a consequencethat there will be two or more PDU segments with the same sequencenumber, since the sequence number is a property of the PDU. The processof segmenting PDUs is also denoted as re-segmentation.

Because of the re-segmentation in LTE, the sequence numbers will notsuffice to identify the data for which ACK or NACK is sent.

SUMMARY

As has emerged from the explanation above, there is a need for asolution by means of which ACKs and NACKs which are transmitted by areceiving party to a sending party in 3G LTE systems can be identified,with respect to the data segments that they are sent in response to.

In addition, another need which should be addressed by the solution inquestion is that it should be possible to send a variable number ofNACKs.

This need is addressed by the present invention in that it discloses amethod for use in a cellular communications system, in which systemtraffic can be exchanged between a first and a second transceiver. Thetraffic in the system is sent in data units, each of which is given anidentifier. The data units may be divided into segments, and a receivingtransceiver may send status information in data frames or data unitsabout properly received, partially received, or non-received data unitsto a sending transceiver, i.e. to the transceiver from which the datawas sent.

According to the method of the invention, in the case of one or morepartially or non-received data units, the status information which issent to the sending transceiver includes information about whether thedata units were non-received or partially received, and in the case of apartially received data unit, which parts of the data units that werenot received.

Thus, by means of the invention, it becomes possible for the receivingtransceiver to distinctly identify non-received parts of data units tothe sending transceiver, thus in turn enabling the sending transceiverto retransmit those parts.

Also, the invention makes it possible to identify more or less anyamount of non-received data, which was another of the needs to beaddressed by the invention.

In one embodiment of the invention, the information about whether or nota data unit was non-received or partially received is included as a flagin said data frames or data units.

In another embodiment, the information about which parts of a data unitthat were non-received is included in the data frames or data units asinformation which indicates a first and a last part of the non-receiveddata.

In yet another aspect of the present invention, in the case that a dataframe or unit from the sending transceiver has been segmented and one ormore last segments has not reached the receiving transceiver, this canbe indicated by the receiving transceiver.

In a further embodiment of the invention, the information about whichparts of a data unit that were non-received is included in the dataframes or data units as information which indicates the identifier ofthe data unit, as well as information about the beginning of thenon-received data in said data unit, and the amount of non-receiveddata.

These and other aspects and advantages of the present invention will beexplained in more detail in the detailed explanation given below.

The invention also discloses a transceiver for use in a system of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail in the following, withreference to the appended drawings, in which

FIG. 1 shows a schematic view of a system in which the invention may beapplied, and

FIGS. 2-6 show various embodiments of the invention, and

FIG. 7 shows a schematic flow chart of a method of the invention, and

FIG. 8 shows a block diagram of a transceiver of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a system 100 in which the invention maybe applied. As mentioned previously, the invention is mainly intendedfor systems of the 3GPP LTE kind, i.e. Third Generation PartnershipProject, Long Term Evolution systems, sometimes also referred to merelyas LTE systems, but officially in 3GPP known as evolved UTRAN orE-UTRAN. These names will be used interchangeably throughout thisdescription.

As shown in FIG. 1, an LTE system 100 can comprise a number of so calledcells, one of which is shown as 130 in FIG. 1. Each cell in an LTEsystem can accommodate a number of users, sometimes generically referredto as UEs, User Equipments. In FIG. 1, one UE is symbolically shown,with the reference number 120.

LTE systems such as the one 100 in FIG. 1 will also comprise a so called“eNodeB”, evolved NodeB, for each cell. One of the functions of theeNodeB of a cell is to control the traffic to and from users in a cell.In FIG. 1, an eNodeB 110 is shown as the eNodeB for the cell 130.

Traffic from the eNodeB to an UE is referred to as down link traffic, orsimply DL traffic, and traffic from the UEs to the eNodeB is known as uplink traffic, or simply UL traffic.

In LTE systems, an RLC protocol, Radio Link Control, is used forcommunication between the eNodeB and the UEs in a cell.

According to RLC, in LTE systems, traffic between two transceivers, i.e.an UE and its eNodeB is sent in so called PDUs, Protocol Data Units.According to RLC, each PDU is assigned an identifier, a so calledsequence number, which allows both the sending and the receiving partyto identify a PDU.

In the description below, it will be assumed that data PDUs are sent bythe eNodeB, i.e. in DL, and that status PDUs are sent by an UE, i.e. inUL. However, it should be pointed out that this is merely an exampleintended to facilitate the reader's understanding of the invention, theinvention can equally well be applied in the other direction, i.e. DataPDUs in UL and Status PDUs in DL. It can be mentioned here that E-UTRANRLC can operate in different modes, configured by the eNodeB, namelyAcknowledged Mode (AM), Unacknowledged Mode (UM) and transparent mode(TM). The status PDUs are at present only used in AM.

If the eNodeB 110 sends a PDU which contains data to the UE 120, i.e. aso called data PDU, the UE can reply with a so called status PDU, i.e. aPDU which indicates to the eNodeB the reception status of the data inthe data PDU which was sent from the eNodeB.

In the status PDU to the eNodeB, data units which are correctly receivedby the UE is acknowledged by the UE by means of so called ACK messagesor indicators, and data units which are erroneously received, i.e. onlyreceived in part, or not received at all are indicated by the UE bymeans of a so called negative ACK, a NACK. If the eNodeB from which thedata originated receives a NACK in return for transmitted data, theeNodeB will thus know that this information should be retransmitted,usually until an ACK is received. In the case of DL data traffic, a UEwill thus send status PDUs with ACKs and/or NACKs to the eNodeB inresponse to data PDUs from the eNodeB.

The ACKs provide information about up to which sequence number PDUs havebeen correctly received. This can be done either by providing thehighest number of a successfully received PDU, or the first number of anon-received PDU.

In E-UTRAN RLC, data PDUs can be re-segmented, i.e. the payload of apreviously created RLC PDU can, at the time of retransmission, be splitinto segments that are sent separately.

In LTE, it is intended that RLC PDU segments should be identified bymeans of the sequence number of the original RLC PDU, as well as a socalled segmentation offset, SO, which indicates the segments' start inthe original RLC PDU. An ACK or a NACK is sent in the form of thesequence number of the original RLC PDU, but since re-segmentation canoccur, the segments which the ACK or NACK from the UE refers to cannotbe identified uniquely in the eNodeB by means of the sequence number,and not even by means of the SO, due to the fact the segmentation canoccur in several “generations”, i.e. multiple re-segmentations canoccur, and the eNodeB does not know which generation that the ACK/NACKsrefer to.

It is this problem, i.e. identification of ACK/NACK:ed RLC PDU data thatthe invention intends to address.

Different cases can be discerned when it comes to status PDUs:

-   -   a. A status PDU with only one ACK, and no NACKs.    -   b. A status PDU with one ACK and one or more NACKS, which has        two sub-cases:        -   i. One or more of the NACKs are “segment NACKs”.        -   ii. All of the NACKS are non-segment NACKs.

In order to address case “a” above, the invention proposes a status PDUwhich is shown in FIG. 2 with the reference number 200. As shown in FIG.2, the status PDU 200 comprises a D/C-field 210, which indicates if thePDU 200 is a data or a control PDU. As will be understood, a status PDUis a control PDU.

In addition, the status PDU 200 includes an ACK field 220, with the ACKbeing provided in the form of the sequence number, SN, of the RLC PDUwhich the ACK refers to. The status PDU 200 also comprises an indicator,e.g. a flag or bit, shown in FIG. 2 as an “E-bit” 230, which is used toindicate the presence or absence of NACKs in the status PDU 200.

In the case of absence of NACKs in the status PDU, i.e. the case shownin FIG. 2, so called “padding” or “dummy bits” can be used in order toachieve proper alignment of the contents of the status PDU 200. Oneexample of such alignment is so called “octet alignment”, i.e. alignmentwhich is used if the status PDU is divided into data octets. The paddingis shown as 240 in FIG. 2.

Turning now to the case identified as “b-i” above, i.e. where one ormore of the NACKs refer to segmented data units, in other words the casein which the NACKs indicate that a data unit has been partiallyreceived, a concept used by the invention will now be introduced. Thisconcept is here referred to as “Segment Offset pairs” or “SO pairs”,i.e. a data pair, one of which is used to indicate the firstnon-received data octet of the PDU which the NACK refers to, and theother of which is used to indicate the last non-received data octetwhich the NACK refers to. It can be added here that although octets areused to exemplify the invention since octets are used in LTE RLC, theinvention can naturally be used if data is sent in other sizes as well.

An example of a Status PDU format 300 which can handle case “b-i” aboveis shown in FIG. 3. In similarity to the Status PDU format 200 of FIG.2, the Status PDU format 300 comprises a field which indicates if thePDU 300 is a data or a control PDU, and an ACK field with the ACK beingprovided in the form of the sequence number, SN, of the RLC PDU whichthe ACK refers to. The status PDU 300 also comprises an indicator, e.g.a flag or bit, shown in FIG. 3 as an “E-bit”, which is used to indicatethe presence or absence of NACKs in the status PDU 300.

If one or more NACKs is included, as in FIG. 3, each NACK is followed byan “E” bit or flag and an “F” bit or flag, where the E bit/flagindicates if another NACK is present or not, and the F bit/flagindicates if an SO pair is included for the particular NACK or not. Inother words, the F bit/flag can be said to indicate if the data unit towhich the NACK refers was segmented or not, since that is the only casewhen SO pairs are used.

It can also be mentioned that the case of (for example) two missing butnon-consecutive parts of one and the same PDU can be handled by thepresent invention in that one and the same NACK SN will occur twice, butwith different SO pairs.

In similarity to the embodiment of FIG. 2, the ACKs and NACKs of thestatus PDU 300 of FIG. 3 are provided in the form of the sequencenumber, SN, of the RLC PDU which the ACK or NACK refers to, for whichreason the ACK/NACKs are shown as ACK_SN or NACK_SN.

After the last NACK of the status PDU 300 in FIG. 3, the SO pairs areincluded for the NACKs for which the “F” flags/bits were set. Thus, theSO pair shown as SO11 and SO12 “belong” to NACK1_SN, and the SO pairshown as SO21 and SO22 “belong” to NACK2_SN. Also, as shown in FIG. 3,“padding”, PAD, may be used in the status PDU 300 of FIG. 3, in order toobtain octet alignment or some similar purpose.

Returning now to the information comprised in the SO pairs, the first SOin an SO pair indicates the first missing data octet of the PDU, and thelast SO in a pair indicates the last missing data octet in the PDU

It should be pointed out that if the data in the received PDUs, i.e. thePDUs to which the ACK/NACKs refer, is arranged in groups other thanoctets, the invention can of course also be applied to such systems. TheSO pairs would then in a way similar to that described above indicatethe beginning and the end of the data in the PDU to which the NACKrefers.

It can also be added that the status PDUs of the invention can also beexpanded by means of a field, for example after the D/C-field, whichindicates the nature of the status PDU, for example if RLC control PDUsother than STATUS PDUs are used. This field is included in the exampleshown in FIG. 3, indicated as “PDU type”. The same principle, i.e. PDUtype, may be applied in the version shown in FIG. 2.

With continued reference to the status PDUs of the invention, it shouldalso be pointed out that the order of the data fields in the status PDUsshown in FIGS. 2 and 3 are merely examples of suitable embodiments, thedata fields in the status PDU of the invention can be moved to otherpositions in the status PDU without affecting the functionality of theinvention, for example in order to achieve octet alignment. As anexample, in the case with only an ACK and no NACKs, i.e. the embodimentshown in FIG. 2, the status PDU 200 could start with a D/C fieldfollowed by an E bit, followed by padding and lastly the ACK with itssequence number.

Turning now to the case shown as b-ii above, i.e. one or more NACKsrefer to non-received data PDUs, as opposed to partially received dataunits, this is handled in the following manner: the F flag correspondingto those NACKs indicates that no SO pairs are included in the status PDUfor those NACKs.

A special case which is also addressed by the invention is when the lastPDU segment of an RLC PDU has not been received by the UE (stillassuming the case of data PDUS in DL). Assume an example where an RLCPDU with sequence number 10 has been segmented into 3 RLC PDUs, with thePDU segments containing octets 1-10, 11-25 and 26-40, respectively.

Consider now the case in which the UE has received the first twosegments of RLC PDU 10, i.e. octets 1-10 and 11-25, and has alsoreceived the following RLC PDU, i.e. RLC PDU 11, in its entirety, butthe UE has not received the last segment of RLC PDU 10, i.e. octets26-40.

In this case, the UE knows that an RLC segment has been lost, but doesnot know its length, so the UE cannot set the second segmentation offsetvalue in the corresponding SO pair in the status PDU. A solution to thiswhich is proposed by the invention is to let a special value of an SOindicate that the end of the NACK:ed segment is not known. Thus, whenthe eNodeB receives a NACK for RLC PDU 10, a first SO is set to 26 andthe corresponding second SO is set to the special value which tells theeNodeB that all data octets from 26 and forward for RLC PDU 10 need tobe retransmitted.

In some cases, an SO pair is not always necessary to obtain the desiredeffect. As will be shown in the following, by using two bits in the “F”field, a complete identification of the non-received data may beachieved.

This is shown in the example of FIG. 4, in which all four combinationsof two bits in the F field are illustrated, i.e. 00, 01, 10 and 11. Themeanings of each of these combinations are also indicated in FIG. 4, asfollows:

F field Meaning

-   00 The NACK refers to the entire RLC PDU, so no SOs are necessary.-   01 The NACK refers to a first part of the RLC PDU, 1 SO is needed in    order to indicate the last non-received data group, such as, for    example, an octet.-   10 The NACK refers to a last part of the RLC PDU, 1 SO is needed in    order to indicate the first non-received data group, such as, for    example, an octet.-   11 The NACK refers to a middle part of the RLC PDU, 2 SOs are needed    in order to indicate the first and the last non-received data group,    such as, for example, an octet.

It should be pointed out that in the case shown in FIG. 4, in similarityto the embodiments shown previously, a “type field” may be needed inorder to separate status RLC PDUs from other RLC control PDUs.

In another embodiment of the present invention, partially received DLRLC data PDUs are indicated to the eNodeB by the UE in an UL status RLCPDU in a slightly different manner than that shown above, i.e. the SOpairs. In the embodiment in question, the status RLC PDU 500 of which isshown in FIG. 5, the UL status RLC PDU from the UE comprises a NACKfield, shown as 510, and a sequence number field, SN, shown as 520,which indicates the sequence number of the DL RLC data PDU which theNACK refers to. Naturally, in the embodiment 500, the SN can also beincluded together with the NACK, as shown in previous embodiments.

In similarity to the previous embodiments, the embodiment 500 alsoincludes the use of an “E” field, shown as 530 in FIG. 5. However, thesignificance of the E-field, i.e. a bit or a flag, differs slightly fromthat of the previous embodiments: in the embodiment 500 of FIG. 5, theE-field is used to signify if the NACK 510 refers to an entire RLC dataPDU or to data within an RLC data PDU. For example, if the E-fieldequals zero, E=0, this could signify that the NACK 510 refers to theentire RLC data PDU which is identified by the SN 520.

Conversely, if E=0 signifies an entire PDU, then E=1 signifies that theNACK 510 refers to data within the PDU identified by the SN 520. In thiscase, information is included in the status PDU 500 in order for theeNodeB to be able to identify the data in question. This informationregarding data in the embodiment 500 comprises a segment offset value,SO, shown as 540 in FIG. 5. The SO 540 indicates the byte offset or thestart of the non-received DL data. However, as opposed to the previousembodiments, the embodiment 500 does not use SO pairs to indicate thetotality of the non-received data. Instead, the embodiment 500 utilizesa Length Field, LF, 550, the value of which indicates the beginning ofthe non-received data, starting from the SO value 540, up to the lastbyte of the non-received data.

As can be realized, in this embodiment of the invention, i.e. the oneshown in FIG. 5, in order to achieve efficient retransmission from theoriginal sender of the data, the exact number of bytes that should beretransmitted needs to be indicated to the sender. Since LTE RLC PDUscan be quite large (e.g. 32767 bytes), the fields (i.e. SO and LF)needed for indication of the RLC PDU segments would need to be quitelarge as well. However, as will also be realized, in many cases themaximum theoretical size of the SO and LF fields will not need to beutilized, which would thus lead to a waste of data space if the size ofthose fields were made static.

In one embodiment of the present invention, the inventors propose toalleviate this problem, i.e. inefficient use of data space for the SOand LF fields. This embodiment will be described in the following.

In this aspect of the invention, a basic principle is that the SO and LFfield sizes in the RLC status PDU are made adaptive to the needs of thecurrent RLC status PDU. Obviously, it is possible to use two differentsizes for SO and LF, e.g. 6 bits for RSO and 4 bits for RSL. However, inthe subsequent description, it will be assumed that the size is thesame.

If, as proposed in this aspect of the present invention, a dynamiclength field for SO and LF are used, the eNodeB (in the case of data inDL and status messages in UL) must know this length field size in orderto be able to read the status message.

A first way of accomplishing this is to have an additional field in theRLC status PDU message header which is indicative of the size of the SOand LF fields. For example, there could be a field which indicates thatall length fields in the current message are 6 bits. This size coulddiffer from RLC PDU status message to status message.

If SO and LF were to be given different size values, two such lengthfields would be needed, or use could be made of a predefinedrelationship between them, e.g. SO is always x bits longer/shorter thanLF. However, since SO and LF are typically of the same order, thisoptimization might not be required.

According to an alternative aspect of the invention, the explicitindication of the size of the SO and LF fields is superfluous, due to are-arrangement in the RLC PDU status message. In this aspect of theinvention, it is proposed to move the “length fields” SO and LF to theend of the RLC PDU status message, which will be described withreference to FIG. 6.

In the embodiment shown in FIG. 6, the status information for allincluded PDUs is provided first, i.e. SN (segment number), RF(Resegmentation Flag) and an extension bit, “E”. In this way it will bepossible to also include complete PDUs, where no specific segmentinformation needs to be sent. For PDUs where resegmentation hasoccurred, the RF is used to indicate that segment location and lengthinformation follows, and SO and LF are appended to the message frame

Thus, in the embodiment of FIG. 6, the “dynamic” part of the statusmessage, i.e. SO and LF, occurs after the last extension bit E, i.e.after the first E bit with a value which indicates that it is the lastone, such as for example the value “0”. Since the overall message sizein this embodiment needs to be known, for example from a MAC or RLCheader, the receiver knows how many bits are left for the SO and LFfields. It also knows how many SO and LF pairs that will follow afterthe last extension bit. Thus, the receiver can calculate the sizes ofthe SO and LF fields.

If it is a requirement that the RLC status PDU should be byte-aligned,an additional step has to be carried out, in that the number ofremaining bits is also divided by the number of indicated segmentfields. The integer result is used as length, while the remaining bitsare not used. As an example, if the remaining length is 51 bits, andbyte alignment (8 bits) is used, we get the calculation 51/8=6 mod 3.Thus, in this example, 3 bits at the end of the status PDU will not beused.

In the example above, the LF is used to determine the end of an RLC PDUsegment. However, it is would be possible within the scope of thepresent invention to use an absolute offset, in similarity to the SO. Insuch a case, the offset would point to the original position of the lastbyte in the RLC PDU segment.

The status message content might describe the data that is ACK:ed orNACK:ed. Also, a mixture of ACKs and NACKs could be included, with oneor more additional bit(s) to provide a suitable ACK/NACK indicator.

The described status message of FIG. 6 should merely be seen as anexample, additional fields like type flags to indicate whether the PDUcontains data or a status, additional length fields and so on might berequired in some applications, and would be within the scope of thisinvention.

Explicit status information may also be added to the status reports,especially in case the standard or implementation allows multiple typesof states to be reported, e.g. NACK and ACK.

An explicit indication of a status may also be necessary if the LTEsystem is configured to exchange a status report of a single type, e.g.only NACKs. Alternatively, the status report sending entity may receivefrom the PDU sending entity a request for a status report of a certaintype (e.g. NACK only) and would thus generate the status report only forthe subset of received segments that have been not been received.

In a further aspect of the invention, it could be envisioned to send theRLC PDU status message as a separate PDU, or piggybacked with anotherPDU.

FIG. 7 shows a rough flow chart of a method 700 of the invention. Stepswhich are options or alternatives are shown with dashed lines.

As has been indicated in the description above, the method of theinvention is intended for use in a cellular communications system suchas the one 100 of FIG. 1, i.e. a system in which traffic can beexchanged between a first and a second transceiver such as the UE 120and the eNodeB 120.

The traffic in the system 100 is sent in data units, and each of thesedata units is given an identifier. The data units may be divided intosegments, and a receiving transceiver may send status information indata frames or data units about properly received, partially received ornon-received data units to the sending transceiver, i.e. to thetransceiver from which the data was sent.

According to the inventive method 700, as indicated in step 705, in thecase of one or more partially or non-received data unit or units, thestatus information which is sent to the sending transceiver includes, asshown in step 710, information about whether data unit or units werenon-received or partially received, and if so, as shown in step 715, inthe case of one or more partially received data units, which parts ofthose data units that were not received.

In one embodiment of the invention, as shown in step 720, theinformation the information about whether or not a data unit waspartially or non-received is included as a flag in said data frames ordata units.

As indicated in step 725, in a further embodiment of the invention, theinformation about which parts of a data unit that were not received isincluded in said data frames or data units as information whichindicates a first and a last part of the not received data unit.

Step 730 indicates that in one aspect of the invention, if a data frameor unit from the sending transceiver has been segmented or re-segmented,and a last segment has not reached the receiving transceiver, this canbe indicated by the receiving transceiver to the sending transceiver,suitably by means of a special predefined value for the informationabout the last part of the non-received received segments.

Step 735 indicates that in one embodiment of the invention, if a dataframe or unit from the sending transceiver has been segmented and a lastsegment has not reached the receiving transceiver, this can be indicatedby the receiving transceiver to the sending transceiver

As has been indicated previously in this description, and as shown instep 740, the method 700 of the invention may suitably be applied to anLTE, Long Term Evolution, system such as the one 100 which isschematically shown in FIG. 1.

If the inventive method 700 is applied to an LTE system, the data PDUsmay be sent in DL and the corresponding status PDUs will then be sent inUL, as indicated in step 750, in which case the “sending transceiver”mentioned above is the eNodeB of an LTE cell, and the “receivingtransceiver” is a UE User Equipment, of the LTE cell.

Conversely, the invention may equally well be applied so that the dataPDUs may be sent in UL and the corresponding status PDUs will then besent in DL, as indicated in step 745, in which case the “sendingtransceiver” mentioned above is the UE of an LTE cell, and the receivingtransceiver is the eNodeB of the LTE cell.

With reference to the status PDU 300 shown in FIG. 3, it can be pointedout that the information from the receiving transceiver to the sendingtransceiver can be sent as a message which has the possibility ofcomprising one or more of the following:

-   -   Information (D/C) about the nature of the message, e.g. data or        control message,    -   Information (PDU type) about the type of message within said        nature, e.g. a status message in the case of control message,    -   Data (ACK) acknowledging properly received data units or frames        in the form of a certain sequence number,    -   A first extension indicator (E),    -   Data (NACK) regarding an non- or partially received data unit or        frame in the form of a certain sequence number (SN) of said data        unit or frame,    -   A second extension indicator (F),    -   Information about the beginning (SO11, SO21) and end (SO12,        SO22) of non-received data.

In the exemplary status PDU shown in FIG. 3, the first extensionindicator, E, indicates the absence or presence of a set comprisinganother of the first, and second extension indicators, i.e. E and F, anddata, NACK, regarding a partially or non-received data unit or frame, inthe form of the identifier, SN, of the data unit or frame. The secondextension indicator, F, indicates the absence or presence of informationabout the beginning, SO11, SO21, and end, SO21, SO22, of non-receiveddata.

The invention also discloses a transceiver for use in a system in whichthe invention is applied. As has emerged from the description above, theinvention can be applied either when data PDUs are sent in DL and thecorresponding status PDUs are sent in UL, in which case the data sendingtransceiver (in the case of E-UTRAN applications) is the eNodeB and thereceiving transceiver, i.e. the transceiver which transmits status PDUsis the UE, or conversely, when data PDUs are sent in UL and thecorresponding status PDUs are sent in DL, in which case the data sendingtransceiver is the UE and the receiving transceiver, i.e. thetransceiver which transmits status PDUs is the eNodeB. Thus, thetransceiver of the invention may be either an E-UTRAN eNodeB or anE-UTRAN UE.

A schematic block diagram of a generic inventive transceiver 800 for useas an E-UTRAN eNodeB or an E-UTRAN UE is shown in FIG. 8. As indicatedin FIG. 8, the transceiver 800 will comprise an antenna, shown as block810, and will also comprise a receive part 820 and a transmit part 830.In addition, the transceiver 800 also comprises a control means 840 suchas a micro processor, as well as a memory 850. Furthermore, if thetransceiver 800 is to be used as an eNodeB, the transceiver 800 alsocomprises an interface 860 towards other components in the system apartfrom the UEs. Since the interface may not be present if the transceiver800 is a UE, the interface 860 is shown with dashed lines.

The transceiver 800 can use the antenna 810, the receive part 820 andthe transmit part 830 for sending traffic to and receiving traffic froma second transceiver in the system, and the transceiver 800 may use thecontrol means 840 together with the memory 850 for sending said trafficin data units.

The control means 840 and the memory 850 may also be used for givingeach of the data units an identifier, such as for example a sequencenumber, and the same means, i.e. blocks 840 and 850 may be used fordividing the data units into segments.

The inventive transceiver 800 also uses the control means 840, thememory 850, the transmitter 830 and the antenna 810 for sendinginformation in data frames or data units about properly received,partially received or non-received data units to the second transceiver,i.e. to the transceiver from which the data was sent.

In addition, the transceiver 800 can use the control means 840 and thememory 850 for, in the case of one or more non-received or partiallyreceived data units, including information in the status informationabout whether the data unit or units were non-received or partiallyreceived, and in the case of one or more partially received data units,which parts of those data units that that were non-received.

In one embodiment, the means 840 and 850 are used by the transceiver 800for including the information about whether or not a data unit waspartially or non-received as a flag in said data frames or data units.

In addition, in a further embodiment, blocks 840 and 850 are used by thetransceiver for including the information about which parts of a dataunit that were non-received in said data frames or data units asinformation which indicates a first and a last part of the non-receiveddata unit.

In another aspect of the invention, the control means 840, the memory850, the transmitter 830, together with the antenna 810 can be used bythe transceiver 800 for indicating to a sending transceiver if a dataframe or unit from the sending transceiver has been segmented, and alast segment has not reached the transceiver 800.

The indication about a missing segment is suitably carried out by meansof using a special predefined value for the information about the lastpart of the missing segment.

In one embodiment, the control means 840 and the memory 850 can be usedby the transceiver 800 for including the information about which partsof a partially received data unit that were not received in said dataframes or data units as information which indicates the identifier ofthe data unit, as well as information about the beginning of thenon-received data in said data unit, and the amount of non-receiveddata.

In addition, the antenna 810, the transmitter 830, the control means 840and the memory 850 can be used by the inventive transceiver for sendingstatus information to a sending transceiver as a message, such as theone 300 of FIG. 3, which can comprise one or more of the following:

-   -   Information (D/C) about the nature of the message, e.g. data or        control message,    -   Information about the type of message within said nature, e.g. a        status message in the case of a control message,    -   Data (ACK) acknowledging properly received data units or frames        in the form of a certain sequence number,    -   A first extension indicator (E),    -   Data (NACK) regarding a non-received or partially received data        unit or frame, in the form of a certain sequence number,    -   A second extension indicator (F),    -   Information about the beginning (SO11, SO21) and end (SO12,        SO22) of non-received data.

Suitably, the first extension indicator (E) indicates the absence orpresence of a set comprising another of said first (E) and second (F)extension indicators and data (NACK) regarding an partially ornon-received unit or frame in the form of the identifier (SN) of saiddata unit or frame, and said second extension indicator (F) indicatesthe absence or presence of information about the beginning (SO11, SO21)and end (SO12, SO22) of non-received data.

The invention is not limited to the examples of embodiments describedabove and shown in the drawings, but may be freely varied within thescope of the appended claims.

The invention claimed is:
 1. A method for use in a cellularcommunications system comprising: receiving, at a receiving transceiver,data units from a sending transceiver, wherein the data units are eachidentified by an identifier and wherein the data units are divided intosegments; sending status information from the receiving transceiver tothe sending transceiver, about properly received, partially received, ornon-received data units; and wherein sending said status informationcomprises sending a message comprising: data acknowledging properlyreceived data units or frames in the form of a certain sequence number;an extension indicator (E) of a first type; data regarding anon-received or partially received data unit or frame, in the form of acertain sequence number; an extension indicator (F) of a second type,indicating whether the data unit or units were non-received or partiallyreceived; and, in the case of one or more partially received data units,which parts of those data units that were not received, and furtherwherein said extension indicator of the first type indicates the absenceor presence of a set comprising another extension indicator of the firsttype and another extension indicator of the second-type and dataregarding a non-received or partially received data unit or frame in theform of the identifier of said data unit or frame.
 2. The method ofclaim 1, according to which the information about whether or not a dataunit was partially or non-received is included as a flag in said dataframes or data units.
 3. The method of claim 1, according to which theinformation about which parts of a data unit that were not received isincluded in said data frames or data units as information whichindicates a first and a last part of the non-received data unit.
 4. Themethod of claim 1, according to which, if a data frame or unit from thesending transceiver has been segmented and a last segment has notreached the receiving transceiver, this can be indicated by thereceiving transceiver to the sending transceiver.
 5. The method of claim4, according to which said indication about a missing segment is carriedout by means of a special predefined value for the information about thelast part of the missing segment.
 6. The method of claim 1, according towhich the information about which parts of a partially received dataunit that were not received is included in said data frames or dataunits as information which indicates the identifier of the data unit, aswell as information about the beginning of the non-received data in saiddata unit, and the amount of non-received data.
 7. The method of claim1, wherein the system comprises an E-UTRAN system.
 8. The method ofclaim 7, wherein said data unit is an RLC POU, such that said segmentsare RLC PDU segments.
 9. The method of claim 8, wherein the sendingtransceiver is an eNodeB of a E-UTRAN cell, and the receivingtransceiver is a User Equipment (UE) of the E-UTRAN cell.
 10. The methodof claim 8, wherein the sending transceiver is a User Equipment (UE) ofan E-UTRAN cell, and the receiving transceiver is an eNodeB of theE-UTRAN cell.
 11. The method of claim 1, wherein the message comprisesone or more of the following: information identifying the message asbeing a data or control message; information identifying the message asa status type message, at least for control messages; and informationabout the beginning and end of non-received data.
 12. The method ofclaim 11, wherein said extension indicator of the second type indicatesthe absence or presence of information about the beginning and end ofnon-received data.
 13. The method of claim 1, wherein the indicator ofthe first type is a bit.
 14. The method of claim 1, wherein theindicator of the second type is a single bit.
 15. The method of claim 1,wherein the indicator of the second type is two bits.
 16. The method ofclaim 1, wherein the data acknowledging properly received data units orframes is not directly followed in the message by the data regarding anon-received or partially received data unit or frame.
 17. A transceiverfor use in a cellular communications system, said transceivercomprising: means for receiving data units from a sending transceiver,wherein the data units are each identified by an identifier and whereinthe data units are divided into segments; means for sending statusinformation about properly received, partially received or non-receiveddata units to said second transceiver, including means for, in the caseof one or more non-received or partially received data units, sendingthe status information as a message comprising: data acknowledgingproperly received data units or frames in the form of a certain sequencenumber; an extension indicator (E) of a first type; data regarding anon-received or partially received data unit or frame, in the form of acertain sequence number; an extension indicator (F) of a second type,indicating whether the data unit or units were non-received or partiallyreceived; and, in the case of one or more partially received data units,which parts of those data units that were non-received; and wherein saidextension indicator of the first type indicates the absence or presenceof a set comprising another extension indicator of the first type andanother extension indicator of the second type and data regarding apartially or non-received unit or frame in the form of the identifier ofsaid data unit or frame.
 18. The transceiver of claim 17, includingmeans for including the information about whether or not a data unit waspartially or non-received as a flag in said data frames or data units.19. The transceiver of claim 17, including means for including theinformation about which parts of a data unit that were non-received insaid data frames or data units as information which indicates a firstand a last part of the non-received data unit.
 20. The transceiver ofclaim 17, including means for, if a data frame or unit from the sendingtransceiver has been segmented and a last segment has not reached thereceiving transceiver, indicating this to the sending transceiver. 21.The transceiver of claim 20, in which said indication about a missingsegment is carried out by means of using a special predefined value forthe information about the last part of the missing segment.
 22. Thetransceiver of claim 17, including means for including the informationabout information about which parts of a partially received data unitthat were not received in said data frames or data units as informationwhich indicates the identifier of the data unit, as well as informationabout the beginning of the non-received data in said data unit, and theamount of non-received data.
 23. The transceiver of claim 17, whereinthe transceiver is configured for operation in a E-UTRAN system.
 24. Thetransceiver of claim 23, wherein said data unit is an RLC PDU, such thatsaid segments are RLC PDU segments.
 25. The transceiver of claim 23,wherein the transceiver comprises an eNodeB of the E-UTRAN system. 26.The transceiver of claim 23, wherein the transceiver comprises a UserEquipment (UE) of the E-UTRAN system.
 27. The transceiver of claim 17,including means for sending status information to a sending transceiveras a message comprising one or more of the following: informationidentifying the message as a data or control message; informationidentifying the message as a status type message, at least for controlmessages; and information about the beginning and end of non-receivedsegments.
 28. The transceiver of claim 27, wherein said extensionindicator of the second type indicates the absence or presence ofinformation about the beginning and end of non-received data.
 29. Thetransceiver of claim 17, wherein the indicator of the first type is abit.
 30. The transceiver of claim 17, wherein the indicator of thesecond type is a single bit.
 31. The transceiver of claim 17, whereinthe indicator of the second type is two bits.
 32. The transceiver ofclaim 17, wherein the data acknowledging properly received data units orframes is not directly followed in the message by the data regarding anon-received or partially received data unit or frame.